It is often useful in analyzing materials to characterize the response of those materials to incoming light (electromagnetic radiation). Two known coefficients for measuring these properties are absorption and scattering coefficients. An absorption coefficient can be expressed as the property of a medium that describes the amount of absorption of radiation per unit path length within the medium. It can be interpreted as the inverse of the mean free path that a photon will travel before being absorbed (if the absorption coefficient does not vary along the path). The unit quantity for an absorption coefficient is inverse length. A scattering coefficient can be expressed as the property of a medium that describes the amount of scattering of radiation per unit path length for propagation in the medium. It can be interpreted as the inverse of the mean free path that a photon will travel before undergoing scattering (if the scattering coefficient does not vary along the path). The unit quantity for a scattering coefficient is inverse length. Along with the scattering coefficient, an absorption coefficient describes the change in radiation intensity per unit length along the path through the medium.
Existing approaches to obtaining a scattering coefficient, b, involve measuring a volume scattering function using an array of detectors placed at various angles around the scattering material. The scattering coefficient is then calculated by integrating the volume scattering function over all angles. Traditionally, the scattering coefficient is obtained by measuring the extinction coefficient, c, using the relation b=c−a, where a is the absorption coefficient. The extinction coefficient, c, is a constant that predicts the attenuation or dissipation of light at a certain wavelength. In pure water, light is highly absorbed in the infrared region of the light spectrum and poorly absorbed in the blue region. Extinction coefficients are influenced by water absorption, suspended organic and inorganic particles, and dissolved compounds. Thus, the visible color in a water sample is the light that is refracted, reflected or re-emitted by substances in water because it has not been absorbed to produce heat or chemical reactions. The absorption coefficient, a, is also measured and, using the relation b=c−a, the scattering coefficient, b, can be calculated. However, sometimes this method can yield unphysical values of the scattering coefficient, b.
As for the measurement of the absorption coefficients of light in water, U.S. Pat. No. 5,424,840 to C. C. Moore and J. R. V. Zaneveld describes a method that can measure the absorption of chlorophyll for a single wavelength, and which was adapted by C. C. Moore and J. R. V. Zaneveld to be usable for nine discrete wavelengths. The major disadvantages of this device are: (1) it cannot measure the scattering coefficient directly; and (2) the accuracy of the measured absorption coefficient depends on how the scattered light is collected and accounted for. Therefore, there remains a need for a device, system and method for measuring more directly the above coefficients with relative accuracy.